Rose advice needed

Hi, I moved into this property in December and am still sorting the very neglected garden out.
I have bent a main stem over an arch.
Q: It is bare in the middle will new shoots fill it in or am i better to use the new shoot and cut the old one away?
The old has already been cut at the top left of the picture but there are many more new stem growing to the right as well
I will be adding another arch to the right.
Q: should i thin out the stems or just split them over the arches when they are long enough?